Monday, January 21, 2013

Ashland team challenges hypothesis for the success of wetland invader

The common reed, Phragmites
australis, is a serious invasive weed in North American wetlands and one of
the most serious invasive plants in the world.
According to a recent hypothesis, the roots of this plant release a toxic
chemical, gallic acid, which is responsible for its success as an invader. However, a team of Ashland faculty and
students has found no evidence to support this hypothesis in a study that has
just been published in the Journal of Chemical Ecology. The paper, titled “Evidence does not support
a role for gallic acid in Phragmites
australis invasion success,” appears in a special issue of the journal on allelochemical interactions in croplands and natural
settings.

Mei Li, a 2013 Chemistry graduate, conducted research with Dr.
Jeff Weidenhamer showing that contrary to other published reports, gallic acid
breaks down very rapidly in Phragmites
soils. She was also unable to find
evidence for gallic acid in Phragmites soil
collected in North Carolina by Dr. Mason Posner and students in his Marine
Biology class. Mei, working with Dr.
Weidenhamer and Dr. Robert Bergosh, then undertook an investigation of the
chemistry of Phragmites plants from
several populations in North Carolina and Ohio.
She successfully isolated one of the major components of extracts of the
plant, and this compound was identified with the aid of the Chemistry
Department’s new high field NMR spectrometer.
Further work established that Phragmites
plants contain only trace amounts of gallic acid, in contrast to previous
reports that the roots contain and release very high concentrations of this
compound. Junior biology major Joshua Allman (pictured above with Dr. Posner) worked to establish that all of the plant populations
sampled were of the invasive genotype previously reported to contain high
levels of gallic acid.

Students in AU's Marine Biology course collecting someof the samples used in this study.

Dr. Jeff Weidenhamer, lead author of the study, began studying
allelopathy – interactions among plants that are mediated by toxic chemicals –
in graduate school. Much of his research
has been devoted to the development of new methods to improve the understanding
of these chemical interactions. One of
the plants that he has previously studied from the Florida scrub community
appears to produce chemicals that inhibit the germination and growth of
grasses. In that case, he implicated
degradation products of gallic acid and another compound as the cause of these
effects. In this study, he notes that
while the occurrence of high concentrations of gallic acid in some populations
of P. australis can’t be ruled out,
the trace concentrations found in this study show that the release of this
compound cannot be a primary, general explanation for the success of this plant
in wetlands. He concludes, “As we tell
our students, a key point of the scientific method is that research ought to be
repeatable. It was a great experience
for them to participate in and help design experiments to test these recent
findings.”

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